[unreadable] [unreadable] The overall goal of this proposal is to elucidate virus-cell and virus-host interactions leading to programmed cell death (apoptosis) in Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease in mice. In contrast to persistence of non-cytolytic RNA viruses in which the host cell survives, persistence of a lytic RNA virus, such as TMEV, requires continuous cell-to-cell spread and infection. In this circumstance, infection cannot be productive in the host target cell in which the virus persists since greater viral spread will result in cell depletion (of the target and possibly other cells) and the demise of the host. For persistence of lytic RNA viruses there must be either (1) selection of genetic virus variants (quasispecies) that are attenuated in virulence or (2) factor(s) present in the target cell that restrict wild type virus replication. TMEV persistence does not result in attenuating mutations, rather central nervous system (CNS) macrophages in which TMEV persists have been demonstrated to restrict TMEV replication, probably at the level of virion assembly. Moreover, TMEV-infected macrophages undergo apoptosis. Several unintended consequences of TMEV-induced apoptosis in macrophages are: (1) virus persistence due to restricted virus replication, (2) cell-to-cell virus spread (in the face of host immune responses), possibly through phagocytosis of infected apoptotic blebs, and (3) augmentation of host immune responses through an adjuvant effect mediated by caspase-1 and by the high virus antigen-load (restriction virus replication occurs after virus translation). The three specific aims are: (1) Identification of the intrinsic signaling pathway(s) in human MCF-7 cells and murine macrophages that induce apoptosis and restrict TMEV infection. (2) Identify TMEV protein(s) that triggers apoptosis in MCF-7 and murine macrophages, their cognate cellular binding proteins involved in cell death, and the step(s) in the TMEV life cycle that is inhibited by apoptosis. (3) Analysis of effect on TMEV infection of caspase-3 deficiency in caspase-3 mice and treatment with peptide pan-caspase inhibitors on pathogenesis, particularly on CNS persistence and the resultant inflammatory demyelinating pathology. [unreadable] [unreadable] [unreadable]